The mechanical properties of metallic castings are commonly altered by the selective addition of treating agents to the molten metal prior to its being poured into a casting mold. For example, in relatively small controlled amounts, the addition of ferrosilicon is effective to refine the microstructure of cast iron for increased strength, magnesium additive increases the ductility of cast iron, and boron will improve hardenability of steel compositions. However, the effectiveness of some treating agents tends to fade immediately after their introduction into the molten metal and the benefits derived therefrom require a relatively short elapsed time between the introduction of the treating agent into the molten metal and the time at which the molten metal begins to solidify.
Various apparatus and methods have been proposed to minimize such fading. Such methods are exemplified by U.S. Pat. Nos. 2,577,837; 2,822,266; 3,367,395; 3,634,075; and 3,703,922. The method taught in U.S. Pat. No. 3,634,075 is also discussed in the Oct. 28, 1971 issue of IRON AGE. While these methods have generally provided improvements, they have not been completely satisfactory. For example, U.S. Pat. No. 3,703,922 to Dunks et al describes an in-mold process where the treating agent is placed in an intermediate chamber in the mold. A number of solid pieces calculated to provide the desired addition is placed in the chamber and the molten metal is poured at a carefully controlled rate to melt and pick up the treating agent as it flows through this chamber as well as the runners and gating system into the main mold cavity. However, such in-mold process has several disadvantages. The treating agents are provided in preshaped pieces with a number of such pieces approximating the amount of the agent actually required placed in the chamber. Thus, unless the amount of treating agent provided by the preshaped pieces coincides exactly with the amount required for a particular casting, costly waste of unused treating agent or a casting composition varying from the optimum will result. Furthermore, at the end of the pouring operation, a sufficiently large piece of the treating agent must remain to assure that an undissolved agglomeration of the material will not be dragged into the gating system and consequently into the mold cavity. Other undesirable effects might also result from any premature movement of the agglomerate mass within the mold tending to plug or restrict an ingate into the cavity. Also since the amount of treating agent melted by the molten metal is a function of the temperature of the molten metal, the actual quantity of the agents consumed may vary greatly between separate castings from a single pour and even within a single casting.
Other treatment processes are typically directed at adding treating agents into the molten metal in the ladle, ladle lip, or in an open stream between the ladle and the mold. Generally additions of this type are adversely affected by the increased time interval which necessarily occur between such earlier additions and solidification of the molten metal. Also this process exposes the molten metal and treating agent mixture to the atmosphere such that oxidizing may occur before the molten metal enters the casting cavity. This forms drosses, slags and oxides which are carried into the casting cavity by the molten metal and solidifies as impurities in the casting.